111 ISOTOPIC COMPOSITION OF PYTERLITE IN VYBORG (VIIPURI), WIBORG BATHOLITH, RUSSIA TAPANI RÄMÖ RÄMÖ, TAPANI 2001. Isotopic composition of pyterlite in Vyborg (Viipuri), Wiborg batholith, Russia. Bulletin of the Geological Society of Finland 73, Parts 1–2, 111–115. Key words: granites, rapakivi, geochemistry, isotopes, neodymium, lead, Proter- ozoic, Vyborg, Russian Federation Tapani Rämö: Department of Geology, P.O. Box 64, FIN-00014 University of Helsinki, Finland. E-mail:
[email protected] INTRODUCTION 1994). The latter turned out to be quite homoge- neous in terms of Nd and Pb isotopes with a clear Active worldwide research on rapakivi granites Paleoproterozoic signature for all plutons extend- and related mafic and intermediate rocks has ing from the Åland Islands in the west to the Finn- shown that this lithologic assemblage is an impor- ish-Russian border in the east (Rämö 1991). tant tool in the study of the composition of deep The Russian Karelian rapakivi batholiths (Sal- continental crust and subcontinental mantle (see mi and Ulyalegi; Fig. 1a) are situated at the con- Haapala & Rämö 1999 and references therein). In tact zone of the Archean and Paleoproterozoic any one area, the radiogenic isotope composition crustal domains of the Fennoscandian Shield and of the rapakivi granites reflects the overall age of their mixed (Archean-Proterozoic) isotopic signa- the unexposed lithosphere that they occupy (e.g., ture is thus quite understandable. Recent studies Rämö 1991, Neymark et al. 1994, Rämö et al. on the Mesoproterozoic